1. Field of the Invention
The present invention relates to a linear actuator having an internal moving body disposed in a tube and moving along the axis of the tube and an external moving body disposed outside the tube and coupled to the internal moving body by a driving member through a slit formed on the wall of the tube. More specifically the present invention relates to a linear actuator provided with a slider member which is disposed between the external moving body and the wall of the tube and with band guides on both ends of the driving member, or a linear actuator provided with a coupling device which connects the external moving body to a sliding body guided along a predetermined moving path.
2. Description of the Related Art
A linear actuator includes a tube (a cylinder barrel) having an axial slit in the wall and an internal moving body disposed in the bore of the tube and movable along the longitudinal axis of the tube. The movement of the piston is transferred to an external moving body by a driving member which couples the external moving body to the internal moving body through a slit formed on the wall of the tube along the longitudinal axis thereof. Usually, an inner seal band and an outer seal band are disposed on the inner and the outer wall surfaces of the tube along the slit in order to close the inner and the outer openings of the slit.
Linear actuators of this type are disclosed in various publications.
For example;
(A) Japanese Unexamined Utility Model Publication (Kokai) No. 5-62705 discloses a linear actuator including a slider member disposed between the external moving body and the outer wall surface of the tube. The slider member is made of synthetic resin and is fitted into a groove formed on the bottom face of the external moving body (i.e., the face of the external moving body facing the outer wall surface of the tube). Further, in the linear actuator of the '705 publication, the internal moving body and the external moving body are connected to each other by a piston yoke through the slit of the tube, and belt separators (band guides) for guiding the inner and the outer seal bands are attached to both ends of the piston yoke.
(B) Japanese Unexamined Utility Model Publication (Kokai) No. 1-104407 discloses a linear actuator including a slider member. The slider member is accommodated in a groove formed on the bottom face of a sliding body. The sliding body is connected to the external moving body. The slider member in the '407 publication is loosely fitted into the groove and is urged against a sliding face formed on the tube outer wall surface by the adjusting screw fitted to the sliding body. The contact between the slider member and the sliding face is adjusted by the adjusting screw.
(C) Japanese Unexamined Patent Publication (Kokai) No. 56-124711 discloses a linear actuator in which separate slider members for sliding on the side walls of the slit are attached to the yoke which connects the internal moving body to the external moving body.
(D) Japanese Unexamined Patent Publication (Kokai) No. 6-42508 and Japanese Unexamined Utility Model Publication (Kokai) No. 6-30504 disclose linear actuators which include slide tables (external moving bodies) formed integrally with the piston yoke. Separate end members are attached to both longitudinal ends of the slide table and a channel groove, through which the outer seal band passes, extends on the top face of the sliding table in the longitudinal direction. A band cover which closes the aperture of the groove is provided. The band cover includes hook shaped engaging members and is fitted to the channel groove by snap fitting the engaging members into the recesses formed on both of the side walls of the channel groove.
(E) Japanese Unexamined Utility Model Publications (Kokai) No. 62-93405 and No. 63-152003 disclose linear actuators including sliding bodies movable along guide rails. In the '405 publication and the '003 publication, the sliding body is provided with a coupling member extending over and covering the top face of the external moving body. The coupling member is attached to the external moving body by fitting a protruding portion formed on one of the coupling member and the external moving body into a recess formed on the other.
(F) Japanese Unexamined Utility Model Publication (Kokai) No. 6-24207 discloses another type of the coupling device for connecting the external moving body to the sliding body. In the '207 publication, a pin member extending in a direction perpendicular to the direction of the movement of the external moving body (i.e., the direction of the longitudinal axis of the tube) is provided on the external moving body. The coupling member extending from the sliding body and covering the top face of the external moving body is provided with engaging grooves for receiving the pin member of the external moving body. The coupling member is attached to the external moving body by engaging the pin member on the external moving body with the engaging grooves on the coupling member.
In the linear actuator in the publication (A), since the slider member and the band guide are attached to the external moving body separately, the number of the elements increases and the assembly process becomes complicated. Further, the slider member in the linear actuator of the publication (A) is fitted into the groove formed on the external moving body. However, in this case, the fitting condition between the slider member and the groove cannot be adjusted once the slider member has been fitted into the groove and the groove and the slider member must be manufactured with high accuracy in order to obtain satisfactory fitting condition between the slider member and the groove. This causes an increase in the manufacturing cost of the linear actuator. Further, since it is difficult to remove the slider member from the groove once the slider member has been fitted into the groove, the slider member is discarded with the external moving body when the linear actuator is scrapped. This makes it difficult to apply recycling processes suitable for the respective materials and may cause environmental problems.
In the linear actuator of the publication (B), the slider member is loosely inserted into the groove on the bottom face of the external moving body and the slider member apt to fall out from the groove during the assembly process. This is especially true when the sliding body is held in the position where the bottom face is facing downward during the assembly. This sometimes makes the assembly process of the linear actuator complicated. Further, since the adjusting screw is required for adjusting the contact between the slider member and the sliding face, the threaded screw hole must be drilled on the slider member in the publication (B). This also increases the number of the manufacturing steps of the linear actuator.
In the linear actuator of the publication (C), separate sliding members are attached to the piston yoke to reduce the friction between the yoke and the wall of the slit and this also causes an increase in the number of elements and the number of assembly steps.
In the linear actuator of the publication (D), since the separate end members are attached to both ends of the slide table, and band guides for guiding the outer seal band are attached to the bottom faces of the end members, the number of elements and the steps of assembly increases. Further, since the outer seal band in the linear actuator of the publication (C) directly contacts the slide table (the external moving body), wear of the seal band and the slide table occurs. When the wear occurs, dust generated by the wear attaches to the surface of the seal band. This causes deterioration of seal performance of the seal band and a shortening of the service life of the seal band. Further, in the linear actuator of the publication (D), since a scraper is fitted into a groove formed on the bottom surface of the slide table, it is difficult to fit the scraper to the slide table. Further, since the band cover in the publication (D) is fitted to the channel groove by the engagement between the engage members and the side walls of the channel groove, it is difficult to remove the band cover from outside.
Further, in the linear actuator of the publication (E), since the top face of the external moving body is covered by the coupling member which connects the external moving body to the sliding body, a space accommodating the coupling member is required above the top face of the external moving body. Therefore, it is difficult to reduce the height of the linear actuator (i.e., the distance between the outer wall of the tube and the upper face of the coupling member).
In the linear actuator of the publication (F), a pin member is used for connecting the external moving body to the coupling member. Therefore, the number of elements and the number of assembly steps increase. Further, to accommodate the pin member in the external moving body, the thickness of the external moving body must be increased. This also causes an increase in the height of the linear actuator.